US2395991A - Mounting of electrodes in electric discharge tubes - Google Patents

Description

March5, 1946- l A. CHILCQT ETAL 2,395,991 MOUNTING OF ELECTRODES IN ELECTRIC DISCHARGE IUBES Filed Dec. 2 1.1943

Inventors. Mizm;

By mm,

Atiomey.

"for short-wave mounted. at each from one another.

Patented Mar. 5, 1946.

:MOUNTING OFvELECTRODE-S -IN ELECTRIC DISCHARGE TUBES Arthur Leslie Chilcot, Timperley, and Sydney Jackson, Chadderton,'Englarid ApplicationDecenibcr 24, 1943, Scrial No.s51-5 ,,503 I InGreatBritainJuneZZ,.1942

.fIhisdnventlon-relates the :mounting 1ofelec- "trodes inrelectric dischargextubeszandrmore :Particularly toitubeso'f the ;type:in :which atleast one electrode is mounted :at-each end ;of *the en velope.

For certain purposes dischargetubes ;of the usual type-in which all :the electrodes :areicarried by'a common pinch, 'or foot; are :undesirable. Examples of 1 such purposes 'areiwhere discharge tubes are requiredto withstand highzmechanical stress, or to operate underrsuch :a condition, or work, "where inter-electrode .ca pacity-m'ust be 'as low as possible;ifor thesepurposes'the type of tube'in whichan 'electrode is end of the envelopei'is 11107126 preferred. Where'thetube has a'cathode-activated by the deposition thereon "ofani -alkali-vmetal, 'it is also highly desirable that' the tube'fbe of the I double-ended typein 'order thatthe cathode may be maintained 7 at low temperature -Jwhilst other parts of the tube are heatedto ensure that: the

' alkali metalis deposited only on the'cathode,

Where discharge tubes are produced-in quantity by mass production it has been found'neces- 'sary to use such means asinsulating inter-electrode spacers in order to obtain products-having characteristics which vary as littleas'possiible ,If fsuch-means' arenot employed wide variations of "characteristics are 'difficultto f avoid due to relatively small variations of spacing of the electrodes. Wherethe' cathode is to be activated as described:abovesuchespacers are objection'able' owingto the likelihood or the formation thereon of ..conducting films "which would cause electrical leakage "between'the elec trodes held by the spacers.

Themain, object of .the presentfinvention isto the vsame manufacturing process are ;asnearly identical as possible, to; one another in' respectof their characteristics, ,andtwhichi avoids gthe use ofinter-electrode spacers. if

.The characteristics .Lof .such', tubes areito a very great. extent .dependent, on "the spa'cingl'betweenelectrodes and the aim. ofltheinvention is to ensure that such spacing is determinedaccurately without the .use. of interele'ctrodel spacers. LTl'lllS .any. slight :variations .in thecharakzterlstics which ,.may still occu between .Qthe .esevleral ,products .made accordance .with the,- inventionare mainly those which arise-from; other :factors;. such .as

the chemical nature of the cathode surfaceand avillbe relatively-small. 1

" i'lhe invention eis particularly -usfi'1l ior .so-

' called midget, tubes.

rprovideLa formofconstruction .of electric *di'scharge tubes which ensures that 'all "products of I ,offthe tube;

- to. one another.

modifiedlform ofjcathodaaiid According-t0 theinventionanelectric discharge tube comprises a :glass envelope having :arrinternalledge formedby steppingtheiinner diameter of'the wall thereof ,:at least one electrodermount- *ed at one endof said envelope; in pre-determine'd location therein, both by referencerto isaidiledge and to the part of'the wallad jacent'theretq and another'electrode which'is prevented f-rornaundergoing both axial and tilting displacement'by abutment against said ledge and-from undergoinglateral displacement'by contact with' the-part of the wall adjacent to said ledge, whereby said electrodes "are located in 'desired 'spatial relationship l in ac ord nce warm .nrcsnt inve tion a methodof constructing adischargeitubeiineludes the; formation of at least one internal'lfigl in. a glass ,cup -likememberlby stepping the diameter of .thenwall thereof in such; manner that said, ledge facesthe mouth ofsaid'membeyabutting a-jigholding at leastione electrodeiagainrst saidsfledge to prevent both axial: and tilting displacement thereof and :against. the -:part.;; the wall of said cup-likemember adjacent-p129; aid

ledge to prevent lateral displacement, mounting the said electrode in the envelope iwhilst so izheld by the jig; removing said jig, inserting another electrode into-said cup-like member "and; closing the mouth of the' latterimembemn :such amaziner as to hold said other"electrode=in contact with said ledgeto prevent both axialand tilting displacement thereof and with the part of the wall of said member adjacent to 's'a'id 'ledge *to prevent lateral displacementg whereby said-electrodes=are located'in desired spatial-relationship toone'anQther.

R r ngv h a m n in d aw Figurel is a verticalcross sectionalyeyv of a cup-like member forming part oftheenvelqpe of thetube; j

Figure '2 is a; similar view showing thetube in an intermediate-stage ofconstruction; ,Eigure 3, is l a similar view showing-the completed tube; r V w Figures 4, 5 and Bare-views; similar toFi ure 3, showing modifiedforms jof -thetube;

Figure v'7 is a View similar to Figure 1,:S hiJ W- 'ing a slightly different form of cup=like member; Fi r a cup and electrode in a vertical cross sectional view of place during manufacture QEigureLQiS a vertical cross-sectional viewera Figures 10 and 11 Y are views similar to 1 12- ure 3, showing further modified forms of tube.

The invention may be carried into effect according to one form by way of example, see Figures 1, 2, and 3, in the manufacture of a diode valve having a tubular anode and a surrounding hollow cylindrical cathode. A glass cup-like member a (see Figure 1) which is to form the envelope, is formed in a mould which causes the wall of the member to be stepped in diameter, forming an internal ledge b round the wall, facing the mouth of the member. The portion of the wall of larger diameter adjacent to the ledge has an internal diameter equal to that of the cathode and from this portion the wall is made slightly conical, increasing in diameter from the ledge to the mouth, to facilitate removal from the mould and also to ensure that, when in position, only the rim of the cathode is in contact with the wall. This increase in diameter is shown somewhat exaggerated in all the drawings. The ledge b together with the wall portion 0 form an annular re-entrant angle. A hole 12 is blown through the middle of the domed end of the cup like member.

The anode e consists of a small tube of nickel having a support wire 1 of suitable material welded to it. The anode, whilst being mounted, is held in a jig 9 (see Figure 2) having an end which, adjacent to the re-entrant angle, is equal in diameter to that of the cathode and the ji is inserted into the cup-like member so that the Wire ,1 passes through the hole in its domed end. The jig is inserted until such end abuts against the ledge b, and is located against axial movement thereby thus preventing tilting, and for axial alignment the part c of the wall adjacent to the ledge. A glass bead h is now fused to the end of the member a and to the support wire J, thus supporting the anode e rigidly and sealing the hole (1. An exhaust tube i is also fused into the end near to the bead. The ji is then removed leaving the anode accurately located with respect to the ledge b and the adjacent part c of the wall.

The cathode 7' (see Figure 3) is in the form of a hollow cylinder having one end closed and a support wire 7:: of suitable material welded to the centre of such end. The cathode 7' is inserted the . into the cup-like member a so as to surround the anode e until the end of the cathode abuts against the ledge b and also makes contact with the part c of the wall. With the cathode thus held, the open end of the cup-like member is fused on to the cathode support wire, as shown at 1, thereby sealing the end and supportin the cathode rigidly. I

The tube is then exhausted and activated by any method.

In the description which follows of .modifications of the invention, parts which are the same as in Figures 1, 2, and 3, or similar, are given the same or similar reference characters.

In accordance with another embodiment of the invention, see Figure 4, the cathode 'j is carried by a glass dish-shaped member m the support wire is being passed through a central hole in the domed end to which it is sealed by a glass bead n. The cup-like member a is constructed as described for Figures 1 and 2 with its anode e, and its parts are therefore given the same reference characters. In addition it, and the dish-shaped member m, are both provided with integral flanges, formed in the original moulding process r y ubse ent fl rin and the flang s, of both members are finally fused together to form the: complete envelope. The arrangement is such that, when the said flanges are in contact be fore fusing, the rim of the open end of the cath ode is about 0.5 millimetre from the ledge b and. during the operation of fusing suchfianges the members wand m are pushed together in order to force the rim against the ledge. When thus closed the cathode 7' is brought into accurate spatial relationship with the anode 6 both axially and transversely as described for Figures 1, 2 and 3..

In a preferred embodiment of the invention, il-- lustrated in Figure 5, the first cup-like member a is made as in Figure 2, with its anode e but the envelope a is somewhat shorter and is formed with an end flange as in Figure 4. For the cath ode a second cup-like member a is provided having an internal ledge b formed in its wall in like manner to that described above for the member a of Figures 1 and 2. The closed end of the cathode 7' whichis the same as shown in Figure 3, is supported. by abutment against the ledge b and by contact with the adjacent part 0 of the wall. In this case the cathode support wire is replaced by a, conducting lead W, the cathode being supported entirelyby abutment against the two ledges b and b and by contact with the adjacent parts 0 and 0 respectively of the walls when the two cup-like members a and a are joined together.

According to a further embodiment, see Figure 6, the cathode a is mounted in a second glasscup-like member 0, but instead of being sup ported therein by abutment against a ledge and by contact with the adjacent part of the wall, the second cup-like member is provided with internal protuberances, one of which isshown at p with which the cathode makes contact as described in the specification of co-pending patent application No. 515,502.

As stated above, the portion of the wall of the cup-like member a between the ledge b and the mouth is made slightly conical; however, it is desirable that the part 0 adjacent to the ledge 7) should be cylindricalfor a length of about 1 millimetre as shown in Figure '7 where the parts have been exaggerated for clarity. Such a short length, whilst not interfering with the removal of the cuplike member from the mould, eliminates lateral displacement should the rim of the cathode not quite abut against the ledge.

In a modification, see Figure 8, the internal diameter of the wall of each cup-like member at the part 0 adjacent to the ledge b and which prevents lateral displacement is somewhat larger than the diameter of the cathode In this case the associated end q of the cathode is fiared out to equal the full diameter and thus only a thin edge is in contact with the glass. This has the advantage that the area of contactbetween the cathode and the glass is reduced and the oathode may be heated for degassing purposes Without cracking or fusing the glass. This modification may be applied to the construction shown in Figure'5, both ends of the cathode being flared out as shown in Figure 9, where the cathode i is formed with flared ends 1' and 9'3.

The constructions described above lead to the formation of pockets in the space between the electrodes and the envelope, therefore it isdesirable to provide holes in appropriate parts of the wall of the cathode to enable the envelope to be evacuated.

The cathode need not be circular in cross-section but may be of any desired shape provided its 11. A diode valve, the anode of which is accurately located both by spaced reference to an internal ledge formed by stepping the diameter a of the wall of the envelope and also by spaced reference to the part of the Wall adjacent thereto and the cathode of which is prevented from undergoing both axial and tilting displacement by abutment against said ledge and. from undergoing lateral displacement by contact with the said part of the wall of the envelope.

,3 against said ledge and an area of the wall adjacentthereto,

ARTHUR LESLIE CHILCOT. SYDNEY JACKSON.

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